1. Field of Invention
The present invention relates to a soft-start circuit. More particularly, the present invention relates to a soft-start circuit to generate an output voltage with a gradual positive or negative increment to provide a soft-start mechanism.
2. Description of Related Art
When an electronic device is used, it is desirable to extend the time period to fully power the device in order to control the high inrush or surge current at turn on. If the current is not controlled, damage may be done to the device's connectors and components. Accordingly, a soft-start is performed by controlling the ramp-up rate of the applied voltage in order to protect the electronic devices. The soft-start circuit can provide the soft-start mechanism and is widely adopted. However, the accurate control over each voltage step of the ramp-up process and the ramp-up rate is the critical issue concerning to the performance of the soft-start circuit. The conventional soft-start circuit makes use of a plurality of resistors, which are easy to suffer from the temperature effect, to generate the voltage steps during the ramp-up process. Thus, the accuracy of the soft-start circuit with multi-resistor structure is not reliable.
Accordingly, what is needed is a soft-start circuit to generate an output voltage with a gradual positive or negative increment and with high accuracy to provide a soft-start mechanism. The present invention addresses such a need.